The present invention relates to a process for the upgrading of particles in an aqueous coal suspension and in particular to a process for the agglomeration of the coal particles by subjecting them to turbulence in the presence of a binder.
Coal can be classified by size.
Particles larger than, for example, 25 mm are generally called "lumps". Particles of from 150 microns to 25 mm may be referred to as "grains" and particles smaller than 150 microns as "fines". These sizes are not strictly adhered to; for example, the limit between grains and fines may lie between 75 and 250 microns, although a size limit of 100 to 150 microns is of more frequent occurrence. In this specification coal slurries are described which mainly consist of fines, although in some cases grains may be present.
Coal particles in an aqueous slurry are agglomerated by subjecting them to turbulence in the presence of a binder by which the surface of the particles is wetted. When the particles collide owing to the turbulence, they tend to stick together and form loose agglomerates. In certain processes, in which special stirrers are used, the agglomerates can be shaped into spheres or "pellets" which can be further consolidated by hardening them by a heat treatment. Selective agglomeration takes place when an oil-phase binder wets the coal particles in preference to the inorganic particles.
Coal particles in an aqueous slurry have a relatively low monetary value which is generally exceeded several times by the cost of the binder. The quantity of binder used for agglomeration is, therefore, important for the economics of the process. Dosing, or determining the proportion of binder to be used, has hitherto been largely determined by the observations made by the operator during operation.
The primary object of this invention is to provide a more accurate and more efficient dosing method for proportioning the binder.